It might require manual restart of the main application to find the plugins, using Force Close in Application settings.
Main reason why it is distributed separately is to comply with restrictions of copyleft licenses terms.
All plugins provided here are optional, and are not required for deadbeef to function properly.
List of plugins:
Monkey''s Audio decoder (APE)
libMAD MP3 decoder
libsidplay2 SID decoder
libayemu VTX decoder
adplug player (many ADLIB music formats)
AAC+MP4 using FAAD2
WAV,SND and others using libsndfile
ALAC support using reversed decoder by David Hammerton
WMA support using heavily modified rockbox wma decoder
MMS support using libmms
source code is normally available on http://sites.google.com/site/ddbandroid/